@color: deeppink;
@m: margin;
@selector: #wrap;
//注意：一般很少把选择器、属性名定义成变量
* {
    @{m}: 0;
  padding: 0;
}

@{selector} {
  position: relative;
  width: 300px;
  height: 400px;
  border: 1px solid;
  margin: 0 auto;

  .inner {
    position: absolute;
    left: 0;
    right: 0;
    top: 0;
    bottom: 0;
    margin: auto;
    background: @color;
    height: 100px;
    width: 100px;
    &:hover {
      background: pink;
    }
  }
}